

This is it. Most other answers focus on one or two things gitlab does, but the essence of Gitlab is that they provide a platform for the whole development cycle, including planning, design, deployment, monitoring, analytics, incident management, etc.

They can do this by using the best / most fitting open source software for each task and integrating it, also by focusing mostly on kubernetes while still providing enough flexibility for other options. You just don't get to use the whole feature set if you're not on kubernetes.
